The present invention relates to a bending press for bending metal foils, of the type comprising an upper panel disposed above a lower panel, one of these panels being fixed in abutment on its ends while the other panel is mobile and actuated in a vertical plane by drive members likewise located at its two ends, the fixed panel being constituted by a plate comprising an upper part and a lower part defined by two slots symmetrically identical with respect to the median transverse plane of said fixed panel, each slot being defined by an upper wall and a lower wall connected by a bottom, and opening out by an opening on the corresponding lateral edge of said plate.
Japanese Utility Model 2 558 928 describes a bending press of this type, in which the work edges of the upper panel and of the lower panel are deformed along longitudinal lines of curvature curved upwardly under the action of the bending efforts exerted by the drive members, and taken up by the end bearings of the lower part of the panel. During the application of the bending efforts, the lateral ends of the upper part approach the lateral ends of the lower part. In other words, the upper walls of the slots approach the lower walls of the slots, and the region of the bottom of the slots is subjected to considerable and repeated stresses which may irremediably degrade the intrinsic elasticity of the upper part of the lower panel.
This Japanese Utility Model also indicates that the slots are each provided with a mobile member of which the position is adjustable, manually or automatically, inside the slots. This mobile member is directly in contact with the lower and upper walls of the corresponding slot and its displacement makes it possible to virtually limit the depth of said slot and therefore to reduce, as the mobile member approaches the opening, the elasticity of the lower panel.
This mobile member makes it possible to adjust the elasticity of the lower panel depending on the bending efforts to be exerted on a workpiece, in order that the lines of curvature of the two work edges of the upper and lower panels be as parallel as possible.
The bottom of each slot is generally constituted by a curved wall whose ends are tangentially connected respectively to the upper wall and to the lower wall. If the latter are substantially parallel, the curved wall is semi-circular, and if they diverge towards the opening, the curved wall is in the form of a sector less than 180xc2x0. The stresses in the plate are considerable in the immediate vicinity of this curved connecting surface and stress peaks in this area may bring about an irremediable and irreversible degradation of the elasticity of the upper part of the lower panel. In the absence of mobile member, the stresses in the bottom area are compression stresses . These stresses may be transformed into tensile stresses when the mobile member is placed near the bottom. These tensile stresses may bring about cracks when the radius of curvature of the bottom is small.
It is an object of the present invention to propose a bending press as mentioned hereinabove, which can carry out a very large number of bending operations without risk of irreversible damage.
This object is attained by the fact that the bottom of each slot is formed by the inner wall of a through bore made in the plate, said inner wall extending over an angle close to 360xc2x0 in order to distribute the stresses due to the bending over a broader area.
With equal curvature of the bottom, the area subjected to the high stresses of the bending press according to the invention is at least equal to double the high-stress area of present-day bending presses. The punctual stresses are thus reduced and there is less risk of obtaining destructive peaks of punctual stresses. The safety steps limiting the relative displacement of the ends of the upper part with respect to the lower part of the lower panel, the bending forces greater than the nominal forces which bring about abutment of the ends of the upper part on the stops, will not cause additional stresses in the region of the bottom.
According to another characteristic, the plate is reinforced in the region of each bottom by at least one lateral counter-plate presenting a cut-out following the shape of the contour of the bottom and of the slot.
A counter-plate is advantageously arranged on either side of the plate in the region of each bottom.
According to yet another characteristic, a sleeve is fitted tightly in each bore, said sleeve being intended to distribute the bending stresses in the regions of the plate surrounding said bore.